One of the problems frequently encountered during the course of producing petroleum and other fluids from subterranean formations is the inadvertent flow of sand or other mineral particles from the petroleum formation along with the formation fluid being recovered from the producing well. This is a well recognized problem and many undesirable consequences result from this phenomena. The flow of sand into the wellbore causes the creation of a cavity or zone of greatly weakened formation around the perforation of the wellbore, which in severe instances will cause the formation to collapse and destroy the casing and cause loss of the production well. Also, continued production of fluid with simultaneous flow of sand or other abrasive mineral particles will cause the wellbore itself to become plugged which reduces the rate of production of oil from the well and in severe instances will completely terminate further production. Finally, the sand being produced and transported to the surface of the earth along with formation fluids causes abrasive wear of tubular goods and pumps utilized in producing wells, which cause early failure of these expensive components.
The above described problems have long been recognized and many procedures have been disclosed in the prior art for forming barriers to the flow of consolidated sand from formations during the production of formation fluids. Most of these procedures have the common feature of forming a stable permeable zone around the production well which permits fluids to flow freely through the barrier, while restraining the flow of particulate matter such as sand or other particles. One particularly successful technique is referred to in the art as gravel packing, and it utilizes granular materials such as sand or gravel which is placed in a cavity or washed out zone adjacent to the production perforations of a producing well. The gravel placed in the well is restrained from itself moving along with the formation fluids either by a mechanical screen or by cementing the sand grains together using a polymerizable resin to form a solid permeable mass to completely fill the washed out zone in order to form the sand restraining, fluid permeable barrier around the production well.
The use of thermal stimulation techniques has imposed even more severe requirements on sand control techniques utilized in wells completed in oil fields being stimulated by thermal means, e.g. by injection of steam or other hot aqueous fluids into the formation, because the passage of the hot aqueous and frequent by alkaline fluids through the resin-consolidated sand mass causes rapid destruction of many resin matrices used to bind the sand or gravel particles together.
U.S. Pat. Nos. 4,427,069 and 4,428,427 introduced the concept of employing a durable resin formed by polymerizing furfuryl alcohol oligomer on the sand grains for the purpose of forming a stable consolidated sand mass for purposes of controlling sand flow into the producing well. In my pending application Ser. No. 07/135,162 filed Dec. 18, 1987, for "Consolidatable Gravel Pack Method," there is disclosed a method for suspending resin coated gravel or sand in an aqueous saline carrier fluid to prevent the unpolymerized resin coated particles from sticking together during the time they are being transported into the formation in order to form a consolidated gravel pack sand control barrier in the formation adjacent to a producing well. In this application, it was noted that during the time the resin coated sand particles are transported into the zone where the permeable mass is to be formed, abrasive removal of the resin from the sand particles is prevented by incorporation in the carrier fluid of a viscosifying amount of a hydrophilic polymers such as hydroxyethylcellulose.
In applying the above feature, it has been found that the resin coated sand particles can indeed be transported from the mixing means on the surface of the earth via a tubing located in a producing well and placed where they are desired in a cavity or zone adjacent to the producing perforations in an oil well, without removal of a significant portion of the resin coating on the sand particles during the time of mixing and transportation. The viscosity of the carrier fluid becomes a hindrance once the fluid comprising the carrier fluid and the resin coated particles has been located in the well, in that it delays or restricts the proper packing of the resin coated particles in the producing well necessary for subsequent polymerization to produce the desired strong, durable, permeable sand controlling zone.
In view of the foregoing discussion, it can be appreciated that there is a substantial, unfulfilled commercial need for a technique for suspending resin coated gravel or sand particles during the time they are mixed and transported via an injection string in a production well to the zone where it is desired to form a consolidated permeable gravel pack for the purpose of restraining the undesired flow of sand, while later allowing the resin-coated gravel or sand particles to pack closely together in a manner which enhances the formation of a dense, durable, strong permeable consolidated mass such as is necessary to control sand migration during production operations. Ideally, what is needed is a fluid which exhibits sufficient viscosity to prevent abrasive removal of polymer from the gravel particles during transport, which fluid automatically exhibits a significant reduction in viscosity after the resin coated granular material has been placed in the zone where the consolidated mass is to be formed.
The present invention is directed to a novel fluid composition and methods employing this fluid whereby the above mentioned unfulfilled need and objective may be satisfied. The invention is directed toward formulating of a fluid which exhibits sufficient viscosity that it permits transportation of the resin coated gravel into the zone where the permeable mass is to be formed, after which the fluid viscosity is automatically reduced to a significant extent, permitting the resin coated sand grains to come together so they may form a uniform and continuous resin matrix bonding the sand or gravel particles together.